Flyfishing, i.e. the European and American type of "feather-and-line" fishing, utilizes the habit of fish of the trout genus actively to prey on insects. This type of fishing uses artificial bait having characteristics of insects to be preyed upon by the fish. The artificial bait is cast and caused to be floated or sunk into water near the position of the fish without surprising the fish so that it is within the visual field of the fish and induces misunderstanding on the part of the fish so that the fish will prey on the bait and get caught on an incorporated hook.
The mayfly, for example, passes its larval stage in water, and, on emergence, temporarily comes afloat on the water surface before flying into the air. Trout like to prey upon these mayflies on the water surface.
Accordingly, an artificial mayfly bait is a particularly preferred artificial bait because, when seen from under water, it looks like an emergent mayfly afloat on the water surface.
When on the water surface, the body of the emerged mayfly distorts the water surface in a depressed shape and comes afloat on the water surface by surface tension. When the water surface is distorted into a depressed shape the direction of refraction of light is differentiated from the surrounding water surface. As a result, when one looks up from under-water the depressed part in question is viewed with an outstanding contrast with respect to the surrounding water surface. As will now be explained, this phenomenon has to do with total reflection which is caused by a difference between refractive indices of water and air (atmospheric air).
(1) The critical refraction angle of a water surface is 48.8 degrees. Hence, it is impossible to see an object above the water surface if viewed from below at an angle of greater than 48.8 degrees. When viewed from such an angle all that is seen is a relatively dark under-surface of the object.
(2) If the object is viewed from below at an angle less than the critical angle the object can be seen through the water.
The above phenomenon is known as a "fish window." It is a phenomenon by which, for the above-mentioned optical reasons, the shape of an object above the water surface is seen as though through a skylight through the water. That is, the range of view of visual points on the underwater side of an object is that falling within a vertical inverted cone having a conical angle of 97.6 degrees (twice the critical angle).
When an aforesaid depressed portion is on the water surface and viewed from under water as in (1), the surrounding of the depressed portion cannot be seen. But the part of the object falling within the critical angle or cone is characteristically viewed as being of strongly-shining silver.
When the relationship between the depressed part and the visual angle from under water is as set forth in (2) above, the surrounding of the depressed portion is within the critical angle from the visual point, and therefore objects on or above the water surface, such as the sky, can be seen through the water surface. On the other hand, a macro-portion having a viewing point that is outside the critical angle is viewed as a dark region, contrary to the case of (1).
In any case, the depressed portion looks different from the surrounding normal water surface. This gives rise to a high possibility that a fish will consider this to be an important characteristic symbol when the fish discovers an insect afloat on the water surface and makes it a target. Actually, it is known from experience that it is a desirable effect for an artificial bait to reproduce such a characteristic when viewed from under water.
However, in the case of (2), when an object floating on the water surface is viewed from under water it becomes a silhouette. Thus, in many cases, when the wings of an insect are light pervious, a theoretical corollary is that an artificial bait imitating it should also be light pervious. In this respect, the use of a light-pervious sheet material in accordance with this invention provides a perfect effect.
Sometimes fishermen use living mayflies on a hook that is then cast to the target site. The live bait is liable, however, to be forced to drop from the hook by pneumatic resistance and, even if it does not drop off, it has a very low possibility of naturally floating on the water surface. This way of fishing, however, is fundamentally different from "fly fishing" to which the present invention is directed.
The floating ability of artificial bait can be improved by simply reducing the weight of the artificial bait. It is difficult, however, to make artificial bait that resembles a mayfly afloat on the water surface. If its weight is decreased, the artificial bait floats, owing to its buoyancy, but the bait becomes saturated with water, and it apparently differs in appearance from a mayfly floating on the water surface.
To make the artificial bait resemble the mayfly floating on a water surface, it is conceivable to form the artificial bait in a shape resemblying a mayfly and give repellency to its surface. In this case, too, however, it is difficult to float the artificial bait properly because the artificial bait makes contact with the water surface at a plane, and there is ineffective generation of an upward force by surface tension. Furthermore, the water repellency of the surface of the artificial bait is deteriorated within short periods of time, and the artificial bait becomes saturated.
The mayfly has been described in the above description. The same can be said, however, with respect to other floating insects, such as the caddisfly and the stonefly.